Pretty easy to tame. Trap it in a circular form of stone Dino gates, place catapult low if catapult is high the crab will die. Then shoot it with a catapult. Cannons insta kill the crab, do not use cannons up/vo/te so people can see
Your crab is out of HP, and there is no annimal corpses to bring? Just put 10+ sleeping bags not far from the trap and let Karkinos kill you enough times to regain HP (as I calculated - 300 HP per death)
This works only when Kark is not fleeing. Otherwise you need to wait until torpor goes down and crab starts to attack. But this worth it. You won't lose the crab you want!
I just figured out that rocket launchers deal torpor to the karkinos, much like the rock golems, but they die a bit more quicker since they don't have much health and rocket launchers deal a lot of damage.
I understand that all the previous tips submitted were useful, but just in case it was not clear, hit the TOP OF THE CRAB, it will have a special animation if you hit it in the correct spot, and will take only a small amount of boulders to tame, even a high level. (Irrelevant with Cannons)